A jury inquest in Norwich earlier heard Mr Dickerson had warned the helicopter needed to take off "no later than 7pm" because of bad weather.

It did not in fact take off until 7.22pm as Dr Haughey oversaw the hanging of pictures as part of his renovation of Gillingham Hall.

Painter-decorator John Savage, from Newry, Northern Ireland, on Wednesday told the inquest Dr Haughey had been choosing paint colours.

At 7.15pm Mr Hoyle said that the helicopter needed to take off immediately or it would be grounded, Mr Savage said.

"His first response was 'John, I'll get back to you about the colours'," Mr Savage added.

He said Dr Haughey immediately left and Mr Hoyle did not seem "stressed or concerned".

Plasterer Robert Graham said: "They said they needed to take off by 7pm or air traffic control would not let them fly because of the fog.

"It was clear they wanted to go. They kept checking their watches."

Labourer Gary Evans was working near the helipad when the aircraft took off. He said by that point the fog had descended.

He added: "I suddenly heard a loud bang, it was so loud it really shocked me. It was a cracking sound, like an engine backfiring.

"It was about 10 to 15 seconds after the helicopter started to fly off. Afterwards everything was very silent."

Some of the workmen suspected the bang was the helicopter but it was not until police arrived that they fully realised what had happened.

Dr Haughey, 70, who lived at Ballyedmond Castle in Co Down, Northern Ireland, was considered to be one of Ireland's richest men, with estimated wealth in excess of £800 million.

Best known as chairman and founder of Norbrook Laboratories, the largest privately owned pharmaceutical company in the world, father-of-three Dr Haughey had a range of other business interests.

A life peer with a seat in the House of Lords, first on behalf of the Ulster Unionist Party before switching to the Conservative Party, he had also previously sat in the upper house of the Republic of Ireland's parliament, the Seanad.

Coroner Jacqueline Lake said the inquest would focus on events leading up to take-off, the training of the pilots particularly when taking off in low visibility, the weather conditions and the regulation of private helicopters.

An Air Accidents Investigation Branch report has already found that the crash may have been triggered by an error in perception along with a lack of training and procedures.

Barry Dolby, who was also working at the house, watched the helicopter take off.

He said: "I could not believe they took off in that fog.

"I've worked on oil rigs and any time there was a sign of fog we would be stuck until it cleared."